wobbly kitchen Table - from 2 to 3 legs

My inclination would be to:

1) Shorten the long leg--might have to do that at the top where it joins the table.
or
2) Lengthen the short leg, again near the top. You might have to fab a metal bracket.

It's hard to say much more without seeing this table. It's hard to understand how it got that much play in it.

These are a possiblity but I don't know if they have that much adjustment: Leg levelers

It seems like the post have wiggle room in the bases. It does not appear to be one leg longer than the other. Its a 3"3/4" tube in 4" opening. (axp)

One of my previous trailers had that problem. I flipped the legs up side down and re-inserted them and the problem was solved.

Those post-style legs will always loosen because most folks lean on the table, causing the post tubes to deform slightly. After the second post broke, I installed a pair of folding table legs. They were about $20 at a local big-box store. Now, the table is rock solid and, if I wish, the whole table can be carried outside to use there. Since my table top also is part of a bed platform, I had to make sure that with the legs folded, I was able to place the table top in it's bed position. That was easy to do.

I'm a third legger....did it last year and what a difference! Ordered an identical unit to the others (even came with screws) from the factory.